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Morphologies of C60 deposited on a substrate
Journal of Physics and Chemistry of Solids 73 (2012) 1071–1074
Contents lists available at SciVerse ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Morphologies of C60 deposited on a substrate Jason Sallgren, Hui Wang, Samantha L. Leonard, Yun Hang Hu n Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA
a r t i c l e i n f o
abstract
Article history: Received 5 October 2011 Received in revised form 11 May 2012 Accepted 15 May 2012 Available online 23 May 2012
The morphologies of deposited C60 on a copper substrate from a C60-benzene solution were evaluated by using Scanning Electron Microscopy. It was found that the forms of deposited C60 were dependent on the aggregation of C60 in its original solution. During natural vaporization of benzene solution on a copper substrate, independent C60 molecules in the solution assembled into crystal C60 on the substrate, whereas the aggregates of C60 in the solution were remained as amorphous C60 particles on the substrate. However, if spinning was employed during vaporizing solvent, the C60 aggregates were destroyed, leading to the formation of crystal C60. Furthermore, the speed of spinning a substrate can tune the size and shape of deposited C60. & 2012 Elsevier Ltd. All rights reserved.
Keywords: A. Fullerenes B. Crystal growth C. Electron microscopy D. Microstructure
1. Introduction More than twenty years after its initial discovery in 1985 [1], C60 is still an intensely studied form of carbon due to its unique properties and possible applications [2–4]. The properties of solid C60 are strongly dependent on its morphologies [5,6]. C60 is soluble in many solvents such as benzene, hexane, and CS2. Therefore, solid C60 solvates can be prepared via evaporation of solvents from its solution. The nature of the solvent plays an important role on the crystal formation and its morphology and shape [7–10]. Recently, various attempts have been made to prepare stable crystalline C60 nanosize materials with various kinds of morphologies [11,12]. Furthermore, facile routes for the preparation of desired crystalline C60 solid with tunable size and shape are being explored. Shape control of nanostructures can be achieved by the three strategies: crystallization/precipitation, template synthesis, and amphiphilic assembly [12c]. Crystallization and precipitation from appropriate solvents and/or at an interface have been investigated for fullerene crystals [13–15]. For example, Sathish et al. have successfully employed solvents to control microscopic shapes of pure C60 [12c,16]. Their research demonstrated the formation of 2D nanosheets of various shapes (hexagons, rhombi, and mixed polygons) from pure C60 molecules by solvent treatment. Furthermore, tuning shapes of crystalline C60 via liquid–liquid interfacial precipitation (LLIP) method are attracting much attention [11b,12a,17–19]. Several groups revealed the self-slow aggregation of C60 molecules into a small cluster in a pure solvent medium
n
Corresponding author. Tel.:þ 1 906 4872261. E-mail address: [email protected] (Y.H. Hu).
0022-3697/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jpcs.2012.05.011
[20–22]. Chu and his coworkers employed light scattering methods to examine the aggregation of C60 at room-temperature in benzene solution with concentrations near the solubility limit [20,23]. Their observation demonstrated that the aggregates grew exponentially with time. Furthermore, Rudalevige et al. found that the aggregate size increased until the aggregate diameter is approximately 600 nm, at which point sedimentation occurs [21c]. Smith et al. provided thermodynamic evidences to prove the solute aggregation [24]. On the other hand, various techniques were developed for the preparation of C60 films [25–27]. The deposition and characterization of C60 thin films have been widely investigated [28–32]. So far, however, there is no report regarding the effect of C60 aggregation (in its original solution) on the morphology of its deposited solid on a substrate. Because the crystallization of C60 from its solution is dependent on the diffusion of C60 molecules in the solution [33], the difficult diffusion of C60 molecules in its aggregates may inhibit their crystallization during the evaporation of solvent. In other words, the amorphous C60 particles formed via self-aggregation in the solution may remain unchanged in the vaporization precipitation. To test this hypothesis, we evaluate the morphologies of deposited C60 on a copper substrate by vaporizing solvent of C60 solution that contains C60 aggregates. 2. Experimental Preparation of C60-benzene solution: C60 (purity 499%) was purchased from Bucky USA. Benzene (from Fisher Chemicals) was used as a solvent for the preparation of a C60-benzene solution, i.e., 32 mg of C60 was added to 40 ml of benzene (0.8 mg/ml), generating a purple C60-benzene solution.
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Dispersion of C60 on a copper disk: Copper foil (0.025 mm thick) was obtained from Sigma-Aldrich and cut into disks with 1.3 cm diameter. For the dispersion of C60 on the copper disk without spinning, a drop of the C60-benzene solution was placed in the center of the copper disk by using a 5 ml disposable pipet. Once the drop was added to an individual copper disk it was allowed to evaporate at room temperature (about 20 1C). Furthermore, for the spinning dispersion of C60 on a copper disk, an Eppendorf centrifuge (model 5702) was used to spin the copper disk during adding a drop of the C60-benzene solution. The spinning speeds of 100 to 4000 RPMs were employed. Scanning Electron Microscopy (SEM) observation of C60 morphology: Deposited C60 on copper disks were imaged with a Hitachi S-4700 FE-SEM, using an accelerating voltage of 1.5 kV at a working distance of 1.5–1.6 mm. X-ray diffraction (XRD): Deposited C60 on a copper disk was subjected to XRD measurement, which was performed with a Scintag XDS2000 Powder Diffractometer equipped with a Cu Ka source, at 45 kV and 35 mA. The scanning speed was 11/min.
3. Results and discussion It was demonstrated that the aggregates of C60 in its benzene solution grew exponentially with time [20a,23]. Furthermore, it was found that 120 days would be long enough to form large amorphous C60 aggregates in its benzene solution [20b]. Therefore, to evaluate the effect of C60 aggregates (in solution) on the morphologies of deposited C60, we placed a drop of 120-days-old benzene solution of C60 on the copper foil and the C60 solvates was obtained via slow natural-vaporization. The morphologies of the deposited C60 were evaluated by SEM. As shown in Fig. 1, one can see that both C60 crystals and amorphous aggregated C60 were observed (Fig. 1). The amorphous C60 aggregates are spherical
particles. The sizes of the amorphous particles distribute from 50 to 500 nm. The crystals formed in the shape of plates and rod-like structures. The crystal plates are large with a width of about 5 mm and a length of 10 mm. The diameters of the crystal rods are about 1 mm. Those crystals on the copper disks are in good agreement with prior investigations of C60-benzene solutions, in which plates, rods, and branched rods were all present [34,35]. What was not present in those investigations was the presence of amorphous aggregated C60 particles. Furthermore, when a drop of the solution of 3 days old was placed on a copper foil and then naturally evaporated, one can see rod and plate shapes of crystalline C60 with a very small amount of amorphous C60 aggregates (Fig. 2a). The diameter of the amorphous particles is about 50 nm. In contrast, when a fresh-prepared-solution was employed for the deposition, crystal plates without amorphous aggregated C60 particles were observed (Fig. 2b), indicating that the deposition of the fresh-prepared-solution produced only crystal C60. Those results demonstrate that the older the solution is, the more the amorphous aggregates of C60 deposited on the substrate could be obtained. Such a relationship between the size of aggregates and the age of the solution is the same for the aggregation in C60 solutions [21]. Furthermore, the size distribution of the amorphous aggregates on a copper substrate, which was obtained in this work, is similar to the observations for aggregates in solutions [21]. In addition, Rudalevige showed that the largest size aggregate in benzene solutions tended to reach 600 nm, at which point sedimentation could occur [21c]. The largest size of deposited C60 in this work was 500 nm. This shows that the aggregates observed in this study are not larger than any witnessed in solution, implying that the aggregates on the copper disks could be from its original solution. Therefore, we can believe that the aggregated C60 on the copper disks first occurred in solution and were remained during the natural vaporization of solvent. Although the aggregates can be destroyed by some forces (such
Fig. 1. C60 deposited on a copper substrate via natural vaporization of a drop of 120-days-olds C60-benzene solution without spinning.
Fig. 2. C60 deposited on a copper substrate via natural vaporization of a drop of (a) 3-days-old C60-benzene solution without spinning and (b) 0-day-old C60-benzene solution without spinning.
J. Sallgren et al. / Journal of Physics and Chemistry of Solids 73 (2012) 1071–1074
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as simply shaking) [20a], there was not such a force during the natural vaporization. In contrast, if the solvent of a C60-solution drop is vaporized with spinning, the centrifuge force should destroy the aggregates of C60. Indeed, as shown in Figs. 3–5, amorphous C60 aggregates were not formed after the vaporization of 120-days-old C60 solution with spinning, but only C60 crystal plates and rods with various sizes were observed. Those observations clearly demonstrate that the crystal C60 deposited on the copper substrate was formed via packing independent C60 molecules (without aggregation) during solvent vaporization. Therefore, a reasonable formation-mechanism of deposited C60 via natural vaporization can be expressed as follows:
deposited on a copper substrate possesses the same fcc structure as the bulk C60.
In conclusion, the aggregation of C60 in its original solution has strong effects on the morphologies of C60 deposited on a copper substrate from the solution. Independent C60 molecules in benzene solution assembled into fcc crystalline C60 on the substrate during the natural vaporization, whereas the aggregates of C60 in the solution were remained as amorphous C60 particles on the
Furthermore, this mechanism can be easily understood as follows: The crystallization of C60 from its solution is dependent on the diffusion of C60 molecules in the solution [33]. Independent molecules should easily form a crystalline during vaporizing solvent due to their easy diffusion. In contrast, the diffusion of C60 molecules in its aggregates is much more difficult than that in a solution, inhibiting their crystallization. Furthermore, Figs. 3–5 also showed that the sizes of C60 crystal plates or rods decreased with increasing spinning speed. Although both crystal plates and rods of C60 were formed via vaporizing solvent with spinning at 100–1000 RPM, only nano-crystal particles, which have diameters of 50–100 nm, were observed when the spinning speed reached 4000 RPM. Therefore, the high-speedspinning coating of C60 onto a substrate would provide a simple approach for the production of nano-crystal C60 particles. The crystal structure of C60 deposited on a copper disk was further evaluated by XRD. As shown in Fig. 6, one can see that the C60 deposited on a copper substrate has four diffraction peaks corresponding to (111), (220), (311), and (222) reflections of the face-centered cubic (fcc) C60 [36]. This indicates that C60
Fig. 4. C60 deposited on a copper substrate via vaporization of a drop of 120-daysold C60-benzene solution with spinning at 1000 RPM.
Fig. 3. C60 deposited on a copper substrate via vaporization of a drop of 120-days-old C60-benzene solution with spinning at 100 RPM.
Fig. 5. C60 deposited on a copper substrate via vaporization of a drop of 120-daysold C60-benzene solution with spinning at 4000 RPM.
4. Conclusions
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[12]
[13]
[14]
[15]
Fig. 6. XRD pattern of C60 deposited on a copper substrate via natural vaporization of C60-benzene solution.
substrate. However, if spinning was employed during vaporizing solvent, the C60 aggregates were destroyed and only crystal C60 could be formed. The sizes of crystal C60 particles can be tuned by spinning the substrate during vaporization of solvent.
Acknowledgment Jason Sallgren and Samantha Leonard were supported by Charles and Carroll McArthur Research Fellowship Program to do this research. This work was supported by the U.S. National Science Foundation (NSF-CBET-0931587) and the ACS Petroleum Research Fund (PRF-51799-ND10).
[16] [17] [18] [19] [20] [21]
[22]
[23] [24] [25] [26]
References [27] [1] H.W. Kroto, J.R. Heath, S.C.O’ Brien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [2] N.J. Turro, J.Y.C. Chen, E. Sartori, M. Ruzzi, A. Marti, R. Lawler, S. Jockusch, J. Lopez-Gejo, K. Komatsu, Y. Murata, Acc. Chem. Res. 43 (2010) 335. [3] (a) A. McNally, R.J. Forster, T.E. Keyes, Phys. Chem. Chem. Phys. 11 (2009) 848; (b) C.Y. Lan, M.D. Su, J. Phys. Chem. A 111 (2007) 6232. [4] (a) Y.H. Hu, E. Ruckenstein, J. Am. Chem. Soc. 127 (2005) 11277; (b) Y.H Hu, E. Ruckenstein, J. Chem. Phys. 119 (2003) 10073. [5] A.A. El-Barbary, H.I. Lebda, M.A. Kamel, Comput. Mater. Sci. 46 (2009) 128. [6] S. Saito, A. Oshiyama, Phys. Rev. Lett. 66 (1991) 2637. [7] L. Wang, B. Liu, S. Yu, M. Yao, D. Liu, Y. Hou, T. Cui, G. Zou, B. Sundqvist, H. You, D. Zhang, D. Ma, Chem. Mater. 18 (2006) 4190. [8] M. Barrio, D.O. Lo´pez, J.L. Tamarit, P. Espeau, R. Ce´olin, H. Allouchi, Chem. Mater. 15 (2003) 288. [9] F. Michaud, M. Barrio, D.O. Lo´pez, J.L. Tamarit, V. Agafonov, S. Toscani, H. Szwarc, R. Ce´olin, Chem. Mater. 12 (2000) 3595. [10] C. Collins, J. Foulkes, A.D. Bond, J. Klinowski, Phys. Chem. Chem. Phys. 1 (1999) 5323. [11] (a) L. Wang, B. Liu, D. Liu, M. Yao, Y. Hou, S. Yu, T. Cui, D. Li, G. Zou, A. Iwasiewicz, B. Sundqvist, Adv. Mater. 18 (2006) 1883;
[28] [29] [30]
[31] [32] [33] [34]
[35] [36]
(b) Y. Jin, R.J. Curry, J. Sloan, R.A. Hatton, L.C. Chong, N. Blanchard, V. Stolojan, H.W. Kroto, S.R.P. Silva, J. Mater. Chem. 16 (2006) 3715; (c) H. Liu, Y. Li, L. Jiang, H. Luo, S. Xiao, H. Fang, H. Li, D. Zhu, D. Yu, J. Xu, B. Xiang, J. Am. Chem. Soc. 124 (2002) 13370. (a) K. Miyazawa, Y. Kuwasaki, A. Obayashi, M. Kuwabara, J. Mater. Res. 17 (2002) 83; (b) K. Miyazawa, K. Hamamoto, S. Nagata, T. Suga, J. Mater. Res. 18 (2003) 1096; (c) M. Sathish, K. Miyazawa, J.P. Hill, K. Ariga, J. Am. Chem. Soc. 131 (2009) 6372. (a) S. Pekker, A. Ja´nossy, L. Mihaly, O. Chauvet, M. Carrard, L. Forro´, Science 265 (1994) 1077; (b) M.H. Nurmawati, P.K. Ajikumar, R. Renu, C.H. Sow, S. Valiyaveettil, ACS Nano 2 (2008) 1429. (a) T. Hasobe, A.S.D. Sandanayaka, T. Wada, Y. Araki, Chem. Commun. (2008) 3372; (b) H.X. Ji, J.S. Hu, L.J. Wan, Q.X. Tang, W.P. Hu, J. Mater. Chem. 18 (2008) 328. (a) L.C. Chong, J. Solan, G Wagner, S.R.P. Silva, R.J.J. Curry, Mater. Chem. 18 (2008) 3319; (b) J. Geng, W. Zhou, P. Skelton, W. Yue, I.A. Kinloch, A.H. Windle, B.F.G. Johnson, J. Am. Chem. Soc. 130 (2008) 2527. M. Sathish, K. Miyazawa, J. Am. Chem. Soc. 129 (2007) 13816. (a) J. Minato, K. Miyazawa, Carbon 43 (2005) 2837; (b) M. Sathish, K. Miyazawa, T. Sasaki, Chem. Mater. 19 (2007) 2398. H.X. Ji, J.S. Hu, Q.X. Tang, W.G. Song, C.R. Wang, W.P. Hu, L.J. Wan, S.T. Lee, J. Phys. Chem. C 111 (2007) 10498. Y. Zhang, W. Liu, L. Jiang, L. Fan, C. Wang, W. Hu, H. Zhong, Y. Li, S. Yang, J. Mater. Chem. 20 (2010) 953. (a) Q. Ying, J. Marecek, B. Chu, Chem. Phys. Lett. 219 (1994) 214; (b) Q. Ying, J. Marecek, B. Chu, J. Chem. Phys. 101 (1994) 2665. (a) H.N. Ghosh, A.V. Sapre, J.P. Mittal, J. Phys. Chem. 100 (1996) 9439; (b) T. Tomiyama, S. Uchiyama, H. Shinohara, Chem. Phys. Lett. 264 (1997) 143; (c) T. Rudalevige, A.H. Francis, R. Zand, J. Phys. Chem. A 102 (1998) 9797. (a) R.V. Honeychuck, T.W. Cruger, J. Milliken, J. Am. Chem. Soc. 115 (1993) 3034; (b) S. Pekker, G. Faigel, K.G.L. Fodor-Csorba, E. Jakab, M. Tegze, Solid State Commun. 83 (1992) 423; (c) K.L. Chen, M. Elimelech, Langmuir 22 (2006) 10994. Y.P. Sun, B. Ma, C.E. Bunker, B. Liu, J. Am. Chem. 117 (1995) 12705. A.L. Smith, E. Walter, M.V. Korobov, O.L. Gurvich, J. Phys. Chem. 100 (1996) 6775. A. Fartash, Thin Solid Films 323 (1998) 296; [41] G.H. Chen, G.B. Ma, Thin Solid Films 323 (1998) 309. (a) W.M. Tong, D.A.A. Ohiderg, H.K. You, R.S. Williams, S.J. Anz, M.M. Alvarez, R.I. Whetten, Y. Rubio, F.N. Dieterich, J. Phys. Chem. 95 (1991) 4709; (b) X. Zou, S. Zhu, J. Xie, J. Feng, J. Crystal Growth 200 (1999) 441. (a) S. Isoda, H. Kawakubo, S. Nishikawa, O. Wada, Nucl. Instrum. Methods B 112 (1996) 94; (b) X. Shi, X.J. Fan, H.X. Guo, Q. Fu, Solid State Commun. 99 (1996) 445. Y.Z. Li, M. Chander, J.H. Weaver, L.P.F. Chibante, R.E. Smalley, Science 252 (1991) 547. B.J. Benning, F. Stepnyak, J.H. Weaver, Phys. Rev. B 48 (1993) 9086. (a) G. Gensterblum, L.M. Yu, J.J. Pireaux, P.A. Thiry, R. Caudano, J.M. Themlin, S. Bouzidi, F. Coletti, J.M. Debever, Appl. Phys. A 56 (1993) 175; (b) G. Gensterblum, K. Hevesi, B.Y. Han, L.M. Yu, J.J. Pireaux, P.A. Thiry, R. Caudano, A.A. Lucas, Phys. Rev. B 50 (1994) 11981. K. Tanigaki, S. Kuroshima, T.W. Ebbesen, Thin Solid Films 257 (1995) 154. M. Sakurai, H. Tada, K. Saiki, A. Koma, Jpn. J. Appl. Phys. 30 (1991) L1892. P. Byszewski, F.L Diduszko, E. Kowalska, J. Fink-Finowicki, A. Witowski, Appl. Phys. Lett. 61 (1992) 2981. V. Agafonov, R. Ceolin, P.Y. Sizaret, A. Dworkin, D. Andre, H. Szwarc, C. Fabre, A. Rassat, L. Straver, J. Dugue, R. Taylor, A. Zahab, P. Bernier, J. Chem. Phys. 89 (1992) 1879. Y. Saito, N. Suzuki, H. Shinohara, Y. Ando, Jpn. J. Appl. Phys. 30 (1991) 2857. L. Wang, B. Liu, D. Li, M. Yao, S. Yu, Y. Hou, B. Zou, T. Cui, G. Zou, B. Sundqvist, Z. Luo, H. Li, Y. Li, J. Liu, S. Chen, G. Wang, Y. Liu, Appl. Phys. Lett. 91 (2007) 103112.
Contents lists available at SciVerse ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Morphologies of C60 deposited on a substrate Jason Sallgren, Hui Wang, Samantha L. Leonard, Yun Hang Hu n Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA
a r t i c l e i n f o
abstract
Article history: Received 5 October 2011 Received in revised form 11 May 2012 Accepted 15 May 2012 Available online 23 May 2012
The morphologies of deposited C60 on a copper substrate from a C60-benzene solution were evaluated by using Scanning Electron Microscopy. It was found that the forms of deposited C60 were dependent on the aggregation of C60 in its original solution. During natural vaporization of benzene solution on a copper substrate, independent C60 molecules in the solution assembled into crystal C60 on the substrate, whereas the aggregates of C60 in the solution were remained as amorphous C60 particles on the substrate. However, if spinning was employed during vaporizing solvent, the C60 aggregates were destroyed, leading to the formation of crystal C60. Furthermore, the speed of spinning a substrate can tune the size and shape of deposited C60. & 2012 Elsevier Ltd. All rights reserved.
Keywords: A. Fullerenes B. Crystal growth C. Electron microscopy D. Microstructure
1. Introduction More than twenty years after its initial discovery in 1985 [1], C60 is still an intensely studied form of carbon due to its unique properties and possible applications [2–4]. The properties of solid C60 are strongly dependent on its morphologies [5,6]. C60 is soluble in many solvents such as benzene, hexane, and CS2. Therefore, solid C60 solvates can be prepared via evaporation of solvents from its solution. The nature of the solvent plays an important role on the crystal formation and its morphology and shape [7–10]. Recently, various attempts have been made to prepare stable crystalline C60 nanosize materials with various kinds of morphologies [11,12]. Furthermore, facile routes for the preparation of desired crystalline C60 solid with tunable size and shape are being explored. Shape control of nanostructures can be achieved by the three strategies: crystallization/precipitation, template synthesis, and amphiphilic assembly [12c]. Crystallization and precipitation from appropriate solvents and/or at an interface have been investigated for fullerene crystals [13–15]. For example, Sathish et al. have successfully employed solvents to control microscopic shapes of pure C60 [12c,16]. Their research demonstrated the formation of 2D nanosheets of various shapes (hexagons, rhombi, and mixed polygons) from pure C60 molecules by solvent treatment. Furthermore, tuning shapes of crystalline C60 via liquid–liquid interfacial precipitation (LLIP) method are attracting much attention [11b,12a,17–19]. Several groups revealed the self-slow aggregation of C60 molecules into a small cluster in a pure solvent medium
n
Corresponding author. Tel.:þ 1 906 4872261. E-mail address: [email protected] (Y.H. Hu).
0022-3697/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jpcs.2012.05.011
[20–22]. Chu and his coworkers employed light scattering methods to examine the aggregation of C60 at room-temperature in benzene solution with concentrations near the solubility limit [20,23]. Their observation demonstrated that the aggregates grew exponentially with time. Furthermore, Rudalevige et al. found that the aggregate size increased until the aggregate diameter is approximately 600 nm, at which point sedimentation occurs [21c]. Smith et al. provided thermodynamic evidences to prove the solute aggregation [24]. On the other hand, various techniques were developed for the preparation of C60 films [25–27]. The deposition and characterization of C60 thin films have been widely investigated [28–32]. So far, however, there is no report regarding the effect of C60 aggregation (in its original solution) on the morphology of its deposited solid on a substrate. Because the crystallization of C60 from its solution is dependent on the diffusion of C60 molecules in the solution [33], the difficult diffusion of C60 molecules in its aggregates may inhibit their crystallization during the evaporation of solvent. In other words, the amorphous C60 particles formed via self-aggregation in the solution may remain unchanged in the vaporization precipitation. To test this hypothesis, we evaluate the morphologies of deposited C60 on a copper substrate by vaporizing solvent of C60 solution that contains C60 aggregates. 2. Experimental Preparation of C60-benzene solution: C60 (purity 499%) was purchased from Bucky USA. Benzene (from Fisher Chemicals) was used as a solvent for the preparation of a C60-benzene solution, i.e., 32 mg of C60 was added to 40 ml of benzene (0.8 mg/ml), generating a purple C60-benzene solution.
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Dispersion of C60 on a copper disk: Copper foil (0.025 mm thick) was obtained from Sigma-Aldrich and cut into disks with 1.3 cm diameter. For the dispersion of C60 on the copper disk without spinning, a drop of the C60-benzene solution was placed in the center of the copper disk by using a 5 ml disposable pipet. Once the drop was added to an individual copper disk it was allowed to evaporate at room temperature (about 20 1C). Furthermore, for the spinning dispersion of C60 on a copper disk, an Eppendorf centrifuge (model 5702) was used to spin the copper disk during adding a drop of the C60-benzene solution. The spinning speeds of 100 to 4000 RPMs were employed. Scanning Electron Microscopy (SEM) observation of C60 morphology: Deposited C60 on copper disks were imaged with a Hitachi S-4700 FE-SEM, using an accelerating voltage of 1.5 kV at a working distance of 1.5–1.6 mm. X-ray diffraction (XRD): Deposited C60 on a copper disk was subjected to XRD measurement, which was performed with a Scintag XDS2000 Powder Diffractometer equipped with a Cu Ka source, at 45 kV and 35 mA. The scanning speed was 11/min.
3. Results and discussion It was demonstrated that the aggregates of C60 in its benzene solution grew exponentially with time [20a,23]. Furthermore, it was found that 120 days would be long enough to form large amorphous C60 aggregates in its benzene solution [20b]. Therefore, to evaluate the effect of C60 aggregates (in solution) on the morphologies of deposited C60, we placed a drop of 120-days-old benzene solution of C60 on the copper foil and the C60 solvates was obtained via slow natural-vaporization. The morphologies of the deposited C60 were evaluated by SEM. As shown in Fig. 1, one can see that both C60 crystals and amorphous aggregated C60 were observed (Fig. 1). The amorphous C60 aggregates are spherical
particles. The sizes of the amorphous particles distribute from 50 to 500 nm. The crystals formed in the shape of plates and rod-like structures. The crystal plates are large with a width of about 5 mm and a length of 10 mm. The diameters of the crystal rods are about 1 mm. Those crystals on the copper disks are in good agreement with prior investigations of C60-benzene solutions, in which plates, rods, and branched rods were all present [34,35]. What was not present in those investigations was the presence of amorphous aggregated C60 particles. Furthermore, when a drop of the solution of 3 days old was placed on a copper foil and then naturally evaporated, one can see rod and plate shapes of crystalline C60 with a very small amount of amorphous C60 aggregates (Fig. 2a). The diameter of the amorphous particles is about 50 nm. In contrast, when a fresh-prepared-solution was employed for the deposition, crystal plates without amorphous aggregated C60 particles were observed (Fig. 2b), indicating that the deposition of the fresh-prepared-solution produced only crystal C60. Those results demonstrate that the older the solution is, the more the amorphous aggregates of C60 deposited on the substrate could be obtained. Such a relationship between the size of aggregates and the age of the solution is the same for the aggregation in C60 solutions [21]. Furthermore, the size distribution of the amorphous aggregates on a copper substrate, which was obtained in this work, is similar to the observations for aggregates in solutions [21]. In addition, Rudalevige showed that the largest size aggregate in benzene solutions tended to reach 600 nm, at which point sedimentation could occur [21c]. The largest size of deposited C60 in this work was 500 nm. This shows that the aggregates observed in this study are not larger than any witnessed in solution, implying that the aggregates on the copper disks could be from its original solution. Therefore, we can believe that the aggregated C60 on the copper disks first occurred in solution and were remained during the natural vaporization of solvent. Although the aggregates can be destroyed by some forces (such
Fig. 1. C60 deposited on a copper substrate via natural vaporization of a drop of 120-days-olds C60-benzene solution without spinning.
Fig. 2. C60 deposited on a copper substrate via natural vaporization of a drop of (a) 3-days-old C60-benzene solution without spinning and (b) 0-day-old C60-benzene solution without spinning.
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as simply shaking) [20a], there was not such a force during the natural vaporization. In contrast, if the solvent of a C60-solution drop is vaporized with spinning, the centrifuge force should destroy the aggregates of C60. Indeed, as shown in Figs. 3–5, amorphous C60 aggregates were not formed after the vaporization of 120-days-old C60 solution with spinning, but only C60 crystal plates and rods with various sizes were observed. Those observations clearly demonstrate that the crystal C60 deposited on the copper substrate was formed via packing independent C60 molecules (without aggregation) during solvent vaporization. Therefore, a reasonable formation-mechanism of deposited C60 via natural vaporization can be expressed as follows:
deposited on a copper substrate possesses the same fcc structure as the bulk C60.
In conclusion, the aggregation of C60 in its original solution has strong effects on the morphologies of C60 deposited on a copper substrate from the solution. Independent C60 molecules in benzene solution assembled into fcc crystalline C60 on the substrate during the natural vaporization, whereas the aggregates of C60 in the solution were remained as amorphous C60 particles on the
Furthermore, this mechanism can be easily understood as follows: The crystallization of C60 from its solution is dependent on the diffusion of C60 molecules in the solution [33]. Independent molecules should easily form a crystalline during vaporizing solvent due to their easy diffusion. In contrast, the diffusion of C60 molecules in its aggregates is much more difficult than that in a solution, inhibiting their crystallization. Furthermore, Figs. 3–5 also showed that the sizes of C60 crystal plates or rods decreased with increasing spinning speed. Although both crystal plates and rods of C60 were formed via vaporizing solvent with spinning at 100–1000 RPM, only nano-crystal particles, which have diameters of 50–100 nm, were observed when the spinning speed reached 4000 RPM. Therefore, the high-speedspinning coating of C60 onto a substrate would provide a simple approach for the production of nano-crystal C60 particles. The crystal structure of C60 deposited on a copper disk was further evaluated by XRD. As shown in Fig. 6, one can see that the C60 deposited on a copper substrate has four diffraction peaks corresponding to (111), (220), (311), and (222) reflections of the face-centered cubic (fcc) C60 [36]. This indicates that C60
Fig. 4. C60 deposited on a copper substrate via vaporization of a drop of 120-daysold C60-benzene solution with spinning at 1000 RPM.
Fig. 3. C60 deposited on a copper substrate via vaporization of a drop of 120-days-old C60-benzene solution with spinning at 100 RPM.
Fig. 5. C60 deposited on a copper substrate via vaporization of a drop of 120-daysold C60-benzene solution with spinning at 4000 RPM.
4. Conclusions
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[12]
[13]
[14]
[15]
Fig. 6. XRD pattern of C60 deposited on a copper substrate via natural vaporization of C60-benzene solution.
substrate. However, if spinning was employed during vaporizing solvent, the C60 aggregates were destroyed and only crystal C60 could be formed. The sizes of crystal C60 particles can be tuned by spinning the substrate during vaporization of solvent.
Acknowledgment Jason Sallgren and Samantha Leonard were supported by Charles and Carroll McArthur Research Fellowship Program to do this research. This work was supported by the U.S. National Science Foundation (NSF-CBET-0931587) and the ACS Petroleum Research Fund (PRF-51799-ND10).
[16] [17] [18] [19] [20] [21]
[22]
[23] [24] [25] [26]
References [27] [1] H.W. Kroto, J.R. Heath, S.C.O’ Brien, R.F. Curl, R.E. Smalley, Nature 318 (1985) 162. [2] N.J. Turro, J.Y.C. Chen, E. Sartori, M. Ruzzi, A. Marti, R. Lawler, S. Jockusch, J. Lopez-Gejo, K. Komatsu, Y. Murata, Acc. Chem. Res. 43 (2010) 335. [3] (a) A. McNally, R.J. Forster, T.E. Keyes, Phys. Chem. Chem. Phys. 11 (2009) 848; (b) C.Y. Lan, M.D. Su, J. Phys. Chem. A 111 (2007) 6232. [4] (a) Y.H. Hu, E. Ruckenstein, J. Am. Chem. Soc. 127 (2005) 11277; (b) Y.H Hu, E. Ruckenstein, J. Chem. Phys. 119 (2003) 10073. [5] A.A. El-Barbary, H.I. Lebda, M.A. Kamel, Comput. Mater. Sci. 46 (2009) 128. [6] S. Saito, A. Oshiyama, Phys. Rev. Lett. 66 (1991) 2637. [7] L. Wang, B. Liu, S. Yu, M. Yao, D. Liu, Y. Hou, T. Cui, G. Zou, B. Sundqvist, H. You, D. Zhang, D. Ma, Chem. Mater. 18 (2006) 4190. [8] M. Barrio, D.O. Lo´pez, J.L. Tamarit, P. Espeau, R. Ce´olin, H. Allouchi, Chem. Mater. 15 (2003) 288. [9] F. Michaud, M. Barrio, D.O. Lo´pez, J.L. Tamarit, V. Agafonov, S. Toscani, H. Szwarc, R. Ce´olin, Chem. Mater. 12 (2000) 3595. [10] C. Collins, J. Foulkes, A.D. Bond, J. Klinowski, Phys. Chem. Chem. Phys. 1 (1999) 5323. [11] (a) L. Wang, B. Liu, D. Liu, M. Yao, Y. Hou, S. Yu, T. Cui, D. Li, G. Zou, A. Iwasiewicz, B. Sundqvist, Adv. Mater. 18 (2006) 1883;
[28] [29] [30]
[31] [32] [33] [34]
[35] [36]
(b) Y. Jin, R.J. Curry, J. Sloan, R.A. Hatton, L.C. Chong, N. Blanchard, V. Stolojan, H.W. Kroto, S.R.P. Silva, J. Mater. Chem. 16 (2006) 3715; (c) H. Liu, Y. Li, L. Jiang, H. Luo, S. Xiao, H. Fang, H. Li, D. Zhu, D. Yu, J. Xu, B. Xiang, J. Am. Chem. Soc. 124 (2002) 13370. (a) K. Miyazawa, Y. Kuwasaki, A. Obayashi, M. Kuwabara, J. Mater. Res. 17 (2002) 83; (b) K. Miyazawa, K. Hamamoto, S. Nagata, T. Suga, J. Mater. Res. 18 (2003) 1096; (c) M. Sathish, K. Miyazawa, J.P. Hill, K. Ariga, J. Am. Chem. Soc. 131 (2009) 6372. (a) S. Pekker, A. Ja´nossy, L. Mihaly, O. Chauvet, M. Carrard, L. Forro´, Science 265 (1994) 1077; (b) M.H. Nurmawati, P.K. Ajikumar, R. Renu, C.H. Sow, S. Valiyaveettil, ACS Nano 2 (2008) 1429. (a) T. Hasobe, A.S.D. Sandanayaka, T. Wada, Y. Araki, Chem. Commun. (2008) 3372; (b) H.X. Ji, J.S. Hu, L.J. Wan, Q.X. Tang, W.P. Hu, J. Mater. Chem. 18 (2008) 328. (a) L.C. Chong, J. Solan, G Wagner, S.R.P. Silva, R.J.J. Curry, Mater. Chem. 18 (2008) 3319; (b) J. Geng, W. Zhou, P. Skelton, W. Yue, I.A. Kinloch, A.H. Windle, B.F.G. Johnson, J. Am. Chem. Soc. 130 (2008) 2527. M. Sathish, K. Miyazawa, J. Am. Chem. Soc. 129 (2007) 13816. (a) J. Minato, K. Miyazawa, Carbon 43 (2005) 2837; (b) M. Sathish, K. Miyazawa, T. Sasaki, Chem. Mater. 19 (2007) 2398. H.X. Ji, J.S. Hu, Q.X. Tang, W.G. Song, C.R. Wang, W.P. Hu, L.J. Wan, S.T. Lee, J. Phys. Chem. C 111 (2007) 10498. Y. Zhang, W. Liu, L. Jiang, L. Fan, C. Wang, W. Hu, H. Zhong, Y. Li, S. Yang, J. Mater. Chem. 20 (2010) 953. (a) Q. Ying, J. Marecek, B. Chu, Chem. Phys. Lett. 219 (1994) 214; (b) Q. Ying, J. Marecek, B. Chu, J. Chem. Phys. 101 (1994) 2665. (a) H.N. Ghosh, A.V. Sapre, J.P. Mittal, J. Phys. Chem. 100 (1996) 9439; (b) T. Tomiyama, S. Uchiyama, H. Shinohara, Chem. Phys. Lett. 264 (1997) 143; (c) T. Rudalevige, A.H. Francis, R. Zand, J. Phys. Chem. A 102 (1998) 9797. (a) R.V. Honeychuck, T.W. Cruger, J. Milliken, J. Am. Chem. Soc. 115 (1993) 3034; (b) S. Pekker, G. Faigel, K.G.L. Fodor-Csorba, E. Jakab, M. Tegze, Solid State Commun. 83 (1992) 423; (c) K.L. Chen, M. Elimelech, Langmuir 22 (2006) 10994. Y.P. Sun, B. Ma, C.E. Bunker, B. Liu, J. Am. Chem. 117 (1995) 12705. A.L. Smith, E. Walter, M.V. Korobov, O.L. Gurvich, J. Phys. Chem. 100 (1996) 6775. A. Fartash, Thin Solid Films 323 (1998) 296; [41] G.H. Chen, G.B. Ma, Thin Solid Films 323 (1998) 309. (a) W.M. Tong, D.A.A. Ohiderg, H.K. You, R.S. Williams, S.J. Anz, M.M. Alvarez, R.I. Whetten, Y. Rubio, F.N. Dieterich, J. Phys. Chem. 95 (1991) 4709; (b) X. Zou, S. Zhu, J. Xie, J. Feng, J. Crystal Growth 200 (1999) 441. (a) S. Isoda, H. Kawakubo, S. Nishikawa, O. Wada, Nucl. Instrum. Methods B 112 (1996) 94; (b) X. Shi, X.J. Fan, H.X. Guo, Q. Fu, Solid State Commun. 99 (1996) 445. Y.Z. Li, M. Chander, J.H. Weaver, L.P.F. Chibante, R.E. Smalley, Science 252 (1991) 547. B.J. Benning, F. Stepnyak, J.H. Weaver, Phys. Rev. B 48 (1993) 9086. (a) G. Gensterblum, L.M. Yu, J.J. Pireaux, P.A. Thiry, R. Caudano, J.M. Themlin, S. Bouzidi, F. Coletti, J.M. Debever, Appl. Phys. A 56 (1993) 175; (b) G. Gensterblum, K. Hevesi, B.Y. Han, L.M. Yu, J.J. Pireaux, P.A. Thiry, R. Caudano, A.A. Lucas, Phys. Rev. B 50 (1994) 11981. K. Tanigaki, S. Kuroshima, T.W. Ebbesen, Thin Solid Films 257 (1995) 154. M. Sakurai, H. Tada, K. Saiki, A. Koma, Jpn. J. Appl. Phys. 30 (1991) L1892. P. Byszewski, F.L Diduszko, E. Kowalska, J. Fink-Finowicki, A. Witowski, Appl. Phys. Lett. 61 (1992) 2981. V. Agafonov, R. Ceolin, P.Y. Sizaret, A. Dworkin, D. Andre, H. Szwarc, C. Fabre, A. Rassat, L. Straver, J. Dugue, R. Taylor, A. Zahab, P. Bernier, J. Chem. Phys. 89 (1992) 1879. Y. Saito, N. Suzuki, H. Shinohara, Y. Ando, Jpn. J. Appl. Phys. 30 (1991) 2857. L. Wang, B. Liu, D. Li, M. Yao, S. Yu, Y. Hou, B. Zou, T. Cui, G. Zou, B. Sundqvist, Z. Luo, H. Li, Y. Li, J. Liu, S. Chen, G. Wang, Y. Liu, Appl. Phys. Lett. 91 (2007) 103112.